1. Field of the Invention
The present invention is directed to the field of angioplasty and, more particularly, to a coaxial dilation catheter having improved construction for greater maneuverability.
2. Description of the Prior Art
Angioplasty has gained wide acceptance in recent years as an efficient and effective method for treating certain types of vascular diseases. In particular, angioplasty is widely used for expanding a constricted area or lesion in a coronary artery. It is also used for treatment of lesions in other parts of the vascular system.
The most widely used form of angioplasty makes use of a balloon dilation catheter which is introduced into the patient's vascular system and is positioned across a stenosis. The balloon is inflated by supplying fluid under pressure through an inflation lumen connected to the balloon. The inflation of the balloon imparts a stretching force to the stenosis or artery wall to reestablish an acceptable blood flow through the artery.
There are various types of catheters available and one category of catheter is referred to as an over the wire (OTW) catheter. An OTW catheter is used in conjunction with a separate guide wire to cross a narrowed site in a person's vascular system. In this type of procedure, the guide wire is first advanced through the vasculature to or near the site of the lesion. After the guide wire is properly positioned, the catheter is advanced or guided over the guide wire so that the balloon portion is at the narrowed site.
OTW catheters may have a coaxial construction. The coaxial construction has an inner tube which defines an inner lumen and an outer tube coaxially disposed about the inner tube to define an outer lumen between the walls of the tubes. The inner lumen will typically have a guide wire running therethrough while the outer lumen conveys inflation fluid from the proximal end of the catheter to the inflatable balloon.
One advantage of the coaxial design is that the proximal portion of the outer tube can be formed of a relatively stiff material to provide increased pushability to the catheter. Another advantage is that the outer and inner tubes can be necked down in the distal region of the catheter and under the proximal waist of the balloon to reduce the distal shaft diameter and the profile of the balloon in its deflated state. Additionally, the inner and outer tubes can be necked over their distal lengths so as to increase the distal flexibility of the catheter. A further advantage is that the coaxial design is symmetrically flexible in all directions. In addition, the coaxial design allows a small degree of relative movement to take place between the inner tube and the outer tube when the catheter is bent further enhancing its flexibility.
Coaxial catheters may have various configurations. For example, the inner tube forming the guide wire lumen may continuously extend from the proximal end to the distal end of the catheter. The outer tube may be cut to a length so that it ends under the proximal waist of the balloon or it may be formed such that the balloon continues and completes the outer tube.
In another coaxial configuration, as described in Packard et al., U.S. Pat. No. 4,646,742, the outer tube extends from the proximal end to the distal end of the catheter and the balloon is bonded to the outer tube at both its proximal and distal waists. More specifically, the outer tube has a first predetermined diameter over a majority of its length and tapers down, in a transition zone, to a second predetermined diameter less than the first diameter which extends to the catheter's distal tip. A movable inner tube, coaxially disposed within the outer tube, has a distal end shaped to mate with the inside surface of the outer tube in the transition zone to form a seal when the inner tube is advanced in the distal direction. Ports are formed through the wall of the outer tube in the transition zone to convey inflation fluid to the inflatable balloon. When the inner tube is withdrawn from its sealing position, only a portion of the inflation fluid is available to fill the inflatable balloon and the remaining portion of the fluid perfuses out the distal end of the catheter.
It is desirable to provide a coaxial catheter having a reduced profile while maintaining the axial force required to cross a tight lesion. In addition, it is desirable to provide a coaxial catheter with varying flexibility characteristics in the proximal and distal regions of the catheter.